U.S. patent number 3,981,309 [Application Number 05/535,466] was granted by the patent office on 1976-09-21 for patient stimulating pacer electrode.
This patent grant is currently assigned to American Optical Corporation. Invention is credited to Robert Lee Cannon.
United States Patent |
3,981,309 |
Cannon |
September 21, 1976 |
Patient stimulating pacer electrode
Abstract
A patient stimulating pacer electrode for use with heart pacers
or other like devices. The electrode is constructed in a porous
manner to have large surface area to reduce polarization losses
while simultaneously having small overall dimensions for increasing
stimulation current density and its ability to stimulate.
Electrically conductive powdered metal is subjected to a sintering
process to produce a porous conductive structure which is employed
as the electrode. Conductive fluid from within the patient's body
flows into the interstices of the overall small-dimensioned porous
conductive structure; the resulting fluid-structure interface
comprises a large surface area thereby reducing polarization
losses.
Inventors: |
Cannon; Robert Lee (Waltham,
MA) |
Assignee: |
American Optical Corporation
(Southbridge, MA)
|
Family
ID: |
24134361 |
Appl.
No.: |
05/535,466 |
Filed: |
December 23, 1974 |
Current U.S.
Class: |
607/121;
607/9 |
Current CPC
Class: |
A61N
1/0565 (20130101) |
Current International
Class: |
A61N
1/05 (20060101); A61N 001/04 () |
Field of
Search: |
;128/404,417,418,419P,DIG.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Attorney, Agent or Firm: Berkenstock, Jr.; Howard R. Nealon;
William C.
Claims
What is claimed is:
1. A heart pacer for stimulating the heart of a patient, said pacer
comprising terminal means for connection to said patient's heart,
generator means for providing stimulation impulses on said terminal
means, means for detecting beating action of said patient's heart,
means responsive to operation of said detecting means for
controlling said generator means, means for energizing seriatim
said generator means, said controlling means, and said detecting
means, said terminal means comprising at least one insulated
electrical conductor having two distal ends, one of said distal
ends being electrically connected to and physically connected
adjacent said generator means, the other of said distal ends being
electrically connected to and physically contacting with tissue of
said heart, said other distal end including electrically conductive
porous means having point contact-welded matallic dust particles
for conducting current through said heart tissue in a manner to
decrease polarization losses between said porous means and its
environment and simultaneously increase current density at the
interface of said tissue and said porous means.
2. An electrode system capable of use with an electronic heart
pacer, said system comprising at least one insulated electrical
conductor whose distal ends are electrically connected between
electrical output of said pacer and tissue of said heart, said
tissue-connected distal end comprising electrically conductive
porous means having point contact-welded metallic dust particles
for conducting current from said pacer into said tissue in a manner
to simultaneously decrease polarization losses and increase current
density at the interface of said tissue and said conducting means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an improved electrode
for use in electrical stimulation of patient muscle tissue for
therapeutic purposes. More specifically, the present invention
relates to an improved electrode for use with electronic heart
pacers.
2. Description of Prior Art
Prior art electrodes are related to means for conducting electrical
current to and from patient muscle tissue by contact between tissue
and electrode at some uncontrollable, unspecified point or surface
area of the electrode. Prior art electrodes normally are
constructed to have smooth surfaces and are generally shaped in
cylindrical-like configurations. Examples of prior art electrodes
can be seen in U.S. Pat. Nos. 3,729,008 and 3,825,015. Background
subject matter disclosed in these patents is incorporated herein by
reference.
A shortcoming of prior art electrodes is that they cannot
simultaneously solve two physiologically-related stimulation
problems which confront devices which are employed to stimulate via
electrodes. The first physiological constraint is that the
stimulation threshold presented to a pacer electrode is directly
proportional to electrode area in constant with patient tissue. In
other words, the larger the contact area between heart tissue and
electrode surface, the lower the current density and the higher the
stimulation threshold. Thus, by reducing size of electrodes,
current density can be increased.
However, polarization losses, the losses which are due to the
build-up of charge at the interface between the tissue and the
electrode surface and poled in a direction to oppose current flow,
are inversely proportional to total electrode area. Therefore, if
one designs an electrode to be small in surface area to achieve
high current density, then the polarization losses may become
excessive and prohibit efficient operation of a stimulating system.
This has been and still is a problem of prior art electrodes.
The present invention provides a solution to this problem of the
prior art. The present invention provides structure for
simultaneously solving both problems, and is thereby a major
advance over prior art electrodes.
SUMMARY OF THE INVENTION
The present invention relates to an electrode system capable of use
with an electronic heart pacer. The electronic heart pacer and
electrode system may be capable of implantation within the body of
a patient. The electrode system is constructed from at least one
insulated electrical conductor connected between pacer output and
muscle tissue to be stimulated, and in this particular instance the
heart muscle. The electrically-conductive tissue-contacting distal
end of the electrode is constructed to be a rigid but porous
electrical conductor, and can be constructed from platinum dust.
The resulting porous structure provides a large area of contact
between electrode structure and body fluids, thereby providing an
overall large electrode surface area contact to reduce polarization
problems, while simultaneously permitting reduction in overall
electrode dimensions to increase current density at the area of
contact between tissue wall and electrode structure.
An advantage, among other, of the present invention is that it
permits longer periods of implantable pacer use than otherwise
available, because the ever-depleting energy of implanted batteries
is used more efficiently. The stimulation threshold is lower due to
high current density, and at the same time the polarization losses
are minimized due to a large electrode surface area. With
conventional electrodes, a typical stimulation threshold is two or
three milliamps of current for a duration of one millisecond. This
current level and time duration represent about 75% of the current
drain from a typical implantable pacer's batteries. The present
invention can reduce the 75% current drain figure to about 25% or
less.
It is therefore an object of the present invention to provide an
improved muscle-stimulating electrode system.
It is another object of the present invention to provide an
improved electrode for stimulating the heart of a patient.
It is further object of the present invention to provide an
improved heart pacer system.
It is yet another object of the present invention to provide an
improved electrode pacer system which can simultaneously optimize
heart stimulation threshold requirements and polarization
losses.
Other objects and advantages of the present invention will be
understood after referring to the description of the preferred
embodiments in connection with the following drawings wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a typical heart pacer system;
FIG. 2 depicts a side view of the tissue-contacting cylindrical
distal tip of the electrode system employed in FIG. 1; and
FIG. 3 depicts an illustrative embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, heartbeat detector and control 10, impulse
generator 20, and batteries 40 are represented as being enclosed by
dashed line 50. Dashed line 50 is intended to represent the outline
of heart pacer encapulation suitable for implanting its enclosed
electrical structure within the body of a patient. The structure
within encapsulation 50, is shown in functional connection with
patient's heart 30. Phantom line 60 is thus intended to represent
the outline of the body of the patient.
Impulse generator 20 provides stimulation to heart 30 over
electrode system or catheter system 90. Heartbeat detector and
control 10 is connected to impulse generator 20 by electrical
conductors 80. Batteries 40 power heartbeat detector and control 10
and impulse generator 20 over conductors 70. Conductors 100 are
electrically connected to the heart and provide heartbeat signals
to detector and control 10. U.S. Pat. No. 3,528,428, discloses
pertinent subject matter, describes operation of such a pacing
system, and is incorporated herein by reference.
FIG. 2 depicts a tissue-contacting distal end portion of a catheter
system of the prior art. Electrode 91 and 92 are exposed conductive
metal cylindrical structures whose surface portions contact tissue
surface of the heart at two separate, contact areas or points.
Conductors 91 and 92 provide current flow paths to and from the
heart. Each of these electrodes are electrically connected to
conductors (not shown) within the cylindrical hollow of catheter
system 90. These conductors are mutually insulated from each other,
and may be constructed from coiled springs or other suitable
configurations. Body-compatable material 93 is generally
constructed from silastic rubber and provides insulation between
the enclosed conductors and the patient's blood-vessel environment
outside of enclosure 93.
The surface of conductors or electrodes 91 and 92 are solid and
smooth. The problems associated with solid, smooth surfaces of
these electrodes have been outlined earlier. Briefly, stimulation
threshold presented to a pacer electrode is proportional to area of
the tissue-electrode contact. Current density decreases as contact
area increases, and the lower the current density, the more
difficult stimulation can become. However, polarization losses,
losses due to a reverse build up of potential at the interface
between electrode and heart tissue, are inversely proportional to
area of the interface.
Referring to FIG. 3, an illustrative embodiment of the present
invention is presented. This is a side view of another cylindrical
electrode 91a similar to but smaller than electrode 91 of FIG. 2.
The important diffrences are the electrode 91a is smaller than
electrode 91 and that the structure of 91a has an interstitial
character constructed by a sintering process, or other suitable
process. The resulting porous structure has a very high
multiplicity of interstices thus providing much larger surface area
than otherwise available from a solid-surfaced electrode of
approximately equal overall dimensions. The body fluids in the
blood vessel or other internal environment in which the electrode
system is placed flow into the interstices, thereby providing an
overall large contact area between the electrode surface and the
fluid and/or tissue. This large contact area reduces polarization
losses between the metal electrode and its environment. Because of
the substantially increased (cavernous) surface area due to
porosity, the overall dimensions of the electrode are reduced in
order to increase current density at the contact surface between
tissue and electrode structure. Reduction of the overall dimensions
of the porous electrode of the present invention from a first
electrode size does not result in an electrode surface area smaller
than that area provided by a solid electrode of the first size.
This electrode of the present invention is constructed from
metallic dust, for example platinum dust, that is compressed or
sintered under a high pressure process, resulting in welds at
certain points between the dust particles that come in contact with
one another. The pressure, temperature, and other process variables
are controlled to provide a metal structure having residual inner
spaces, and not to permit a flow of the metal dust into a solid
structure. This sintering process is a form of a welding process.
The resultant surface area is textured similarly to that of a cube
of granulated sugar, for example. The resultant metallic conductor
is then merely employed in place of the prior art smooth surface
conductor 91 and the optimum result of the present invention is
thereby achieved.
The invention may be embodied in yet other specific forms without
departing from the spirit or essential characteristics thereof.
Thus, the present embodiments are to be considered in all respects
as illustrative and not restrictive, the scope of the invention
being indicated by the appended claims rather than by the foregoing
description, and all changes which come within the meaning and
range of equivalency of the claims are therefore intended to be
embraced therein.
* * * * *